A manufacturer that produces iPhones and Nokia and Motorola handsets is offering tens of thousands of pounds to anyone who can prove foul play in the sudden death of a teenage Chinese worker.

FoxConn, a division of the Taiwan electronics company Hon Hai, has announced a reward of 500,000 yuan (£45,000) for information in the case of Ma Xiangqian who was found dead near the stairway of the dormitory of one of its factories in Shenzhen, southern China, on 23 January.

Early stages of the investigation suggested he died of natural causes, but Ma's relatives say they found scars on his body and that the 19-year-old had no previous health problems, the state newspaper China Daily reported.

"There is more to my brother's death than meets the eye. For 19 years my brother had not developed any unusual physical symptoms," the worker's sister Ma Hui told Guangzhou Daily.

She claimed her brother had been picked on for unintentionally damaging company equipment and was later assigned to clean toilets.

A FoxConn spokesman said he had not heard the allegations.

Pathologists conducted a postmortem examination but have yet to release the results. FoxConn said it had invited Ma's family to attend the autopsy.

Li Jinming, the company's administrative general manager, said: "We understand that Ma's family wants to find the real cause behind his death. We are co-operating closely with police authorities and have announced a reward of 500,000 yuan to anyone who can prove there was foul play."

A manager initially told Ma's relatives that he had passed out and was being treated. FoxConn said in a statement that he did this because he wanted to break the news of their son's death to them in person.

It said it would do its best to help the family and said it was dedicated to protecting the rights and safety of its employees.

A spokesman in the firm's Taiwan headquarters told the Guardian: "It is a case involving human life, which is of supreme importance, and so what we can do is hand it over to the police and wait for them to finish the investigation. Before that we have very little we can say."

In a statement, the company said Ma submitted his resignation to the company on 12 January and stopped working eight days later. He had joined the factory in November.

Shenzhen police said they were still investigating the case.

FoxConn said it was making its statement in response to speculation information about the case on the internet, adding that it welcomed "fair monitoring" by the press and public.